package org.apache.lucene.search.spans;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;
import java.lang.reflect.Method;

import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.Term;
import org.apache.lucene.search.MultiTermQuery;
import org.apache.lucene.search.Query;
import org.apache.lucene.search.TopTermsRewrite;
import org.apache.lucene.search.ScoringRewrite;
import org.apache.lucene.search.BooleanClause.Occur; // javadocs only

/**
 * Wraps any {@link MultiTermQuery} as a {@link SpanQuery}, 
 * so it can be nested within other SpanQuery classes.
 * <p>
 * The query is rewritten by default to a {@link SpanOrQuery} containing
 * the expanded terms, but this can be customized. 
 * <p>
 * Example:
 * <blockquote><pre>
 * {@code
 * WildcardQuery wildcard = new WildcardQuery(new Term("field", "bro?n"));
 * SpanQuery spanWildcard = new SpanMultiTermQueryWrapper<WildcardQuery>(wildcard);
 * // do something with spanWildcard, such as use it in a SpanFirstQuery
 * }
 * </pre></blockquote>
 */
public class SpanMultiTermQueryWrapper<Q extends MultiTermQuery> extends SpanQuery {
    protected final Q query;
    private Method getFieldMethod = null, getTermMethod = null;

    /**
     * Create a new SpanMultiTermQueryWrapper. 
     * 
     * @param query Query to wrap.
     * <p>
     * NOTE: This will call {@link MultiTermQuery#setRewriteMethod(MultiTermQuery.RewriteMethod)}
     * on the wrapped <code>query</code>, changing its rewrite method to a suitable one for spans.
     * Be sure to not change the rewrite method on the wrapped query afterwards! Doing so will
     * throw {@link UnsupportedOperationException} on rewriting this query!
     * In Lucene 3.x, MultiTermQuery allows queries to rewrite to different field names, but SpanQuery
     * needs a fixed field. The wrapped query must therefore support getField() or getTerm().
     * @throws IllegalArgumentException if the wrapped query does not provide getField() or getTerm().
     */
    public SpanMultiTermQueryWrapper(Q query) {
        this.query = query;

        MultiTermQuery.RewriteMethod method = query.getRewriteMethod();
        if (method instanceof TopTermsRewrite) {
            final int pqsize = ((TopTermsRewrite) method).getSize();
            setRewriteMethod(new TopTermsSpanBooleanQueryRewrite(pqsize));
        } else {
            setRewriteMethod(SCORING_SPAN_QUERY_REWRITE);
        }

        // In Lucene 3.x, MTQ has no fixed field, we need to get it by reflection.
        // If the underlying query does not allow to get a constant field, we throw IAE:
        try {
            getFieldMethod = query.getClass().getMethod("getField");
        } catch (Exception e1) {
            try {
                getTermMethod = query.getClass().getMethod("getTerm");
            } catch (Exception e2) {
                try {
                    getTermMethod = query.getClass().getMethod("getPrefix");
                } catch (Exception e3) {
                    throw new IllegalArgumentException("SpanMultiTermQueryWrapper can only wrap MultiTermQueries" + " that can return a field name using getField() or getTerm()");
                }
            }
        }
    }

    /**
     * Expert: returns the rewriteMethod
     */
    public final SpanRewriteMethod getRewriteMethod() {
        final MultiTermQuery.RewriteMethod m = query.getRewriteMethod();
        if (!(m instanceof SpanRewriteMethod))
            throw new UnsupportedOperationException("You can only use SpanMultiTermQueryWrapper with a suitable SpanRewriteMethod.");
        return (SpanRewriteMethod) m;
    }

    /**
     * Expert: sets the rewrite method. This only makes sense
     * to be a span rewrite method.
     */
    public final void setRewriteMethod(SpanRewriteMethod rewriteMethod) {
        query.setRewriteMethod(rewriteMethod);
    }

    @Override
    public Spans getSpans(IndexReader reader) throws IOException {
        throw new UnsupportedOperationException("Query should have been rewritten");
    }

    @Override
    public String getField() {
        try {
            if (getFieldMethod != null) {
                return (String) getFieldMethod.invoke(query);
            } else {
                assert getTermMethod != null;
                return ((Term) getTermMethod.invoke(query)).field();
            }
        } catch (Exception e) {
            throw new RuntimeException("Cannot invoke getField() or getTerm() on wrapped query.", e);
        }
    }

    @Override
    public String toString(String field) {
        StringBuilder builder = new StringBuilder();
        builder.append("SpanMultiTermQueryWrapper(");
        builder.append(query.toString(field));
        builder.append(")");
        return builder.toString();
    }

    @Override
    public Query rewrite(IndexReader reader) throws IOException {
        final Query q = query.rewrite(reader);
        if (!(q instanceof SpanQuery))
            throw new UnsupportedOperationException("You can only use SpanMultiTermQueryWrapper with a suitable SpanRewriteMethod.");
        return q;
    }

    @Override
    public int hashCode() {
        return 31 * query.hashCode();
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        final SpanMultiTermQueryWrapper other = (SpanMultiTermQueryWrapper) obj;
        return query.equals(other.query);
    }

    /** Abstract class that defines how the query is rewritten. */
    public static abstract class SpanRewriteMethod extends MultiTermQuery.RewriteMethod {
        @Override
        public abstract SpanQuery rewrite(IndexReader reader, MultiTermQuery query) throws IOException;
    }

    /**
     * A rewrite method that first translates each term into a SpanTermQuery in a
     * {@link Occur#SHOULD} clause in a BooleanQuery, and keeps the
     * scores as computed by the query.
     * 
     * @see #setRewriteMethod
     */
    public final static SpanRewriteMethod SCORING_SPAN_QUERY_REWRITE = new SpanRewriteMethod() {
        private final ScoringRewrite<SpanOrQuery> delegate = new ScoringRewrite<SpanOrQuery>() {
            @Override
            protected SpanOrQuery getTopLevelQuery() {
                return new SpanOrQuery();
            }

            @Override
            protected void addClause(SpanOrQuery topLevel, Term term, float boost) {
                final SpanTermQuery q = new SpanTermQuery(term);
                q.setBoost(boost);
                topLevel.addClause(q);
            }
        };

        @Override
        public SpanQuery rewrite(IndexReader reader, MultiTermQuery query) throws IOException {
            return delegate.rewrite(reader, query);
        }

        // Make sure we are still a singleton even after deserializing
        protected Object readResolve() {
            return SCORING_SPAN_QUERY_REWRITE;
        }
    };

    /**
     * A rewrite method that first translates each term into a SpanTermQuery in a
     * {@link Occur#SHOULD} clause in a BooleanQuery, and keeps the
     * scores as computed by the query.
     * 
     * <p>
     * This rewrite method only uses the top scoring terms so it will not overflow
     * the boolean max clause count.
     * 
     * @see #setRewriteMethod
     */
    public static final class TopTermsSpanBooleanQueryRewrite extends SpanRewriteMethod {
        private final TopTermsRewrite<SpanOrQuery> delegate;

        /** 
         * Create a TopTermsSpanBooleanQueryRewrite for 
         * at most <code>size</code> terms.
         */
        public TopTermsSpanBooleanQueryRewrite(int size) {
            delegate = new TopTermsRewrite<SpanOrQuery>(size) {
                @Override
                protected int getMaxSize() {
                    return Integer.MAX_VALUE;
                }

                @Override
                protected SpanOrQuery getTopLevelQuery() {
                    return new SpanOrQuery();
                }

                @Override
                protected void addClause(SpanOrQuery topLevel, Term term, float boost) {
                    final SpanTermQuery q = new SpanTermQuery(term);
                    q.setBoost(boost);
                    topLevel.addClause(q);
                }
            };
        }

        /** return the maximum priority queue size */
        public int getSize() {
            return delegate.getSize();
        }

        @Override
        public SpanQuery rewrite(IndexReader reader, MultiTermQuery query) throws IOException {
            return delegate.rewrite(reader, query);
        }

        @Override
        public int hashCode() {
            return 31 * delegate.hashCode();
        }

        @Override
        public boolean equals(Object obj) {
            if (this == obj)
                return true;
            if (obj == null)
                return false;
            if (getClass() != obj.getClass())
                return false;
            final TopTermsSpanBooleanQueryRewrite other = (TopTermsSpanBooleanQueryRewrite) obj;
            return delegate.equals(other.delegate);
        }

    }

}
